The Effect of Amino Sugars on the Water Vapor Permeability and the Mobility of Water in Nafion(R) Membranes

Yuichi HIRATA, Yutaka MIURA and Tsutomu NAKAGAWA*

Department of Industrial Chemistry, Meiji University; Higashi-mita, Tama-ku, Kawasak-shi 214-8571 Japan

The influence of the state of water on the water vapor permeability through different cation forms of the Nafion(R) membranes was studied. Two alkali metals (Na and K) and two amino sugars (an equimolar mixture of α-D-glucopyranosyl-(1→6)-2-amino-2-deoxy-α-D-mannitol and its D-glucitol (GPA) and D-glucosamine (GLU)) were used as counter ions. Based on the two state-model, the content and mobility of non-freezing water were determined using DSC and 17O-NMR. The water vapor permeability of the Nafion membranes depended on the solubility of water in the membrane while the diffusivity of water vapor through the Nafion(R) membranes was related to the mobility of non-freezing water rather than water uptake in the membranes. The diffusivity of water through the Nafion(R) membrane containing GPA was the lowest value in this study because, for the membrane, the fraction of non-freezing water was the greatest and the mobility of non-freezing water was the lowest. The uptake of freezing water in the Nafion membrane was depressed by the bulky structure of amino sugars and the mobility of non-freezing water around amino sugars was lowered by local aggregation of the hydroxyl group of amino sugars compared to other counter ions.

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